1. Field of the Invention
The present invention relates to an antifuse and, more particularly, to an antifuse with a silicide layer overlying a diffusion region.
2. Description of the Related Art
Unlike a fuse which, when programmed, changes from a low-resistance to a high-resistance device that substantially blocks a current from flowing through the device, an antifuse is a device which, when programmed, changes from a high-resistance to a low-resistance device that allows a current to flow through the device.
FIG. 1 shows a cross-sectional drawing that illustrates a conventional antifuse 100. As shown in FIG. 1, antifuse 100 includes a N+ diffusion region 112 which is formed in a p-type substrate 110, and surrounded by isolating field oxide regions FOX.
In addition, as further shown in FIG. 1, antifuse 100 also includes an ONO (oxide-nitride-oxide) dielectric layer 114 which is formed on diffusion region 112, and a layer of N+ doped polysilicon (poly) 116 which is formed on dielectric layer 114.
In operation, due to the presence of dielectric layer 114, no current can flow from poly layer 116 to diffusion region 112 (or in the opposite direction) when normal operating voltages are applied to antifuse 100. This condition is typically referred to as the unprogrammed state.
On the other hand, when a strong electric field is established across dielectric layer 114, such as when a 16.5 volt pulse is applied to poly layer 116 while diffusion region 112 is grounded, dielectric layer 114 breaks down, thereby forming a conductive path between poly layer 116 and diffusion region 112. This condition, which is typically referred to as the programmed state, allows current to flow between poly layer 116 and region 112 when normal operating voltages are again applied to antifuse 100.
One of the problems with antifuse 100 is that, when incorporated into a circuit, such as a field programmable gate array, high voltage transistors must also be incorporated into the circuit to handle the high voltages (16.5V) which are required to program antifuse 100. The incorporation of high voltage transistors, in turn, increases the complexity and cost of the fabrication process used to produce the circuit.
Although programming voltages as low as 10.6 volts (with a nitride-oxide dielectric thickness of 65 .ANG.) have been reported in the literature (see Chen et al., A Sublithographic Antifuse Structure for Field Programmable Gate Array Applications, IEEE Electron Device Letters, Vol. 13, No. 1, January 1992), it is desirable to have antifuses which can be programmed with much lower voltages, such as at or below the supply voltage, e.g., at or below 3.3V in a 0.35 micron process.